Thanks for your answer ! Following your idea, ny playing around in maxima, I found that :
trigreduce(sin((a+b)/c)) ----> sin(b/c+a/c) Therefore trigexpand(trigreduce(sin((a+b)/c))) ----> cos(a/c)*sin(b/c)+sin(a/c)*cos(b/c) Which is what is wanted but I did not find any trigreduce in sage Any idea how I can do that directly in sage ? On 2 fév, 16:15, kcrisman <[email protected]> wrote: > Dear Nicolas, > > If you do > > sage: a = sin((a+b)/c) > sage: a.trig_expand?? > > you will see the source code, which simply uses one of Maxima's > expansion routines, whose behavior should be documented on the Maxima > Sourceforge site. My suspicion is that Maxima declines to expand this > because c might be zero, though there could be another reason. We > have several Maxima experts who also read this list and might have > more detailed information, but this would be the first place I would > start. One idea might be to apply another simplification/expansion to > whatever you feed into your trig functions, before you expand the > rest. > > Good luck, and please follow up with more details, or specific > proposals for how we can improve our documentation to help make it > clearer how this works. Thank you! > > - kcrisman > > On Feb 2, 9:06 am, Nicolas <[email protected]> wrote: > > > Here is some to-my-opinion strange behaviour of trig_expand : > > > #Declare real variables > > var('a b c') > > assume([a,'real'],[b,'real'],[c,'real']) > > assumptions() > > ---> [a is real, b is real, c is real] > > > #Case 1 > > sin(a+b).trig_expand() > > ---> sin(a)*cos(b) + sin(b)*cos(a) > > > #Case 2 > > sin((a+b)/2).trig_expand() > > ---> sin(1/2*a)*cos(1/2*b) + sin(1/2*b)*cos(1/2*a) > > > #Case 3 > > sin((a+b)/c).trig_expand() > > ---> sin((a + b)/c) > > > #Case 4 > > sin((a/c+b/c)).trig_expand() > > > ________ > > In case 3, the expansion is not done. I wonder if it would be possible > > to do it. Obviously, if the sine argument was rational expanded before > > trig expansion, it would work but none seem to work on the whole > > expression. > > > Any idea ? > > > PS: I am actually using this in an expression where doing this > > expansion would simplify a lot and I would have expected simplify_full > > to see it... which it does not, I suspect because of this. > > ---> sin(a/c)*cos(b/c) + sin(b/c)*cos(a/c) -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
